/Engine/Source/Runtime/AnimGraphRuntime/Public/KismetAnimationLibrary.h
This function calculates the velocity of a position changing over time. You need to hook up a valid PositionHistory variable to this for storage.
static float K2_CalculateVelocityFromPositionHistory ( float DeltaSeconds, FVector Position, [FPositionHistory](API\Runtime\AnimGraphRuntime\FPositionHistory) & History, int32 NumberOfSamples, float VelocityMin, float VelocityMax )